1. Field of the Invention
The present invention relates to a piezoelectric device.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication Nos. 2010-103194 and 2006-286911 disclose a piezoelectric device including a dielectric film and a pair of electrode films that sandwich the dielectric film. The electrode films are composed of a noble metal such as Au, Pt, or Ir. When the dielectric film serves as a piezoelectric film, a dielectric film composed of lead zirconate titanate (PZT) containing Pb is generally used.
In recent years, “lead-free” industrial products have been urgently demanded to protect the environment, and thus existing piezoelectric materials are increasingly replaced with lead-free piezoelectric materials. An example of a promising lead-free piezoelectric material is a potassium sodium niobate (KNN)-based piezoelectric material disclosed in Japanese Unexamined Patent Application Publication No. 2007-320840.
However, many lead-free piezoelectric materials provide a piezoelectric film having a small displacement and low reliability. Among such lead-free piezoelectric materials, the piezoelectricity of a KNN-based piezoelectric material has been improved. However, such a KNN-based piezoelectric material does not have a large displacement unlike PZT-based piezoelectric materials. In addition, the KNN-based piezoelectric material has low moisture resistance and thus the piezoelectricity is degraded when the KNN-based piezoelectric material is exposed to a high-humidity environment.
In the case of lead zirconate titanate (PZT), if a base metal element such as Ni is used for electrodes, Pb that is one of main components constituting lead zirconate titanate (PZT) is present in the form of a metal and the base metal element such as Ni that is a material for electrodes is present in the form of an oxide from the viewpoint of the relationship of oxidation-reduction potential between the piezoelectric material and the electrode. This poses a problem in that the life and reliability of piezoelectric devices are decreased. Therefore, when a Pb-containing piezoelectric material is used, a noble metal needs to be used for electrodes, which makes it difficult to reduce the cost.